This invention relates generally to electrical cabinets and more particularly to cooling systems used cool electrical components stored in such cabinets.
As is known in the art, air is typically used to cool electrical components stored in electrical cabinets. One technique used for such cooling is to provide apertures through the top of a cabinet. Fans are mounted in registration with the apertures to create an air flow which passes over the electrical components. However, if one of the fans fails to operate properly, air external of the cabinet can re-circulate into the interior of the cabinet. The re-circulating air may cause the failed fan to "backdrive" (spin backwards) and give a visual appearance of operating (spinning). In some cases, the speed of the fan backdriving can exceed a tachometer alarm output speed, causing the fan alarm signal to appear normal. Some fans with low horsepower motors will continue to backdrive after a temporary power failure or a hot swap of the fan module, because the fan motors are unable to overcome the backdriving torque caused by the in-rushing air momentum re-circulating through the fan.
Re-circulating air through the failed fan or "short circuiting" can provide a path of least resistance to the adjacent fans and thus lower the cabinet airflow impedance. This in turn lowers the operating point (pressure/volume relationship) of the fans and causes less pressure to be generated and less air volume through the cabinet. Areas of high impedance in the cabinet are most effected in terms of airflow reduction. The loss in cabinet pressure and airflow contribute to less cooling and higher component temperatures which can accelerate component failure.